This invention relates to an electrode used in an electronic instrument, such as an electrocardiograph, adapted to measure the state of a living body, and more particularly to a clip-type electrode used in an electrocardiograph.
An electrocardiograph is widely utilized to diagnose the heart of a human or other living body. In operation, a minute electric current induced in the surface of the skin of, e.g., the human body, is applied to an electrocardiograph composed of electronic circuitry external to the body. The electrocardiograph measures and observes changes in electrical potential caused by changes in the minute current ascribable to the heartbeat. Based on the results of such analysis, the doctor can make a diagnosis on whether or not the patient's heart is functioning normally.
FIG. 1 shows a system for measuring changes in electrical potential by using an electrocardiograph. In the drawing, numeral 1 designates an electrocardiograph composed of electronic circuitry. A lead 2 is connected from the electrocardiograph 1 to an electrical distributor 3 from which four leads 4.sub.1, 4.sub.2, 4.sub.3, and 4.sub.4 are connected to one end of respective clip-type electrodes 5.sub.1, 5.sub.2, 5.sub.3 and 5.sub.4 clipped to the wrists and ankles of a patient lying lengthwise on a bed, not shown. The other ends of the clip-type electrodes 5.sub.1, 5.sub.2, 5.sub.3 and 5.sub.4 are respectively connected to leads 6.sub.1, 6.sub.2, 6.sub.3 and 6.sub.4 and thence to a display unit 7 such as a CRT.
In the above-described system, changes in the electrical potential induced in the wrists and ankles of the human body are sensed by the clip-type electrodes 5.sub.1, 5.sub.2, 5.sub.3 and 5.sub.4 and displayed by the display unit 7. Based on the voltage waveform on the display unit, the doctor may make a diagnosis on whether the heart function is normal or abnormal.
In the foregoing system, the wrists and ankles to which the clip-type electrodes 5.sub.1, 5.sub.2, 5.sub.3 and 5.sub.4 are attached are not truly cylindrical in shape and differ in thickness from one patient to another. The thickness also differs with one and the same patient depending on the positions at which the electrodes 5.sub.1 to 5.sub.4 are attached.
FIG. 2 shows the construction of a prior-art clip-type electrode. As shown, the electrode 5' comprises a pair of curved clamping plates 8, 8' adapted to be clipped on limb such as a wrist or ankle. These plates 8, 8' are biased by a spring 5b disposed on a shaft 5a so that the ends of the plates are caused to approach each other. An electrode plate 9 is affixed to the inner surface of the clamping plate 8 by a fastener such as nut. A pair of terminals 10, 10' provided on the outside of the clamping plate 8 are connected to the electrode plate 9.
The above described clip-type electrode 5' is manually grasped at the rear part of the clamping plates 8, 8' so that the forward parts of the clamping plates 8, 8' are opened by pivoting about the shaft 5a for attachment to a limb such as the wrist or ankle of the human body.
As mentioned above, the wrist or ankle of the human body has a cross-sectional configuration and thickness that differ from one individual to another. When a wrist or ankle is clamped by the clamping plates 8, 8', no particular problem is encountered if the wrist or ankle of the individual has a thickness which enables the spring 5b to apply a clamping force of appropriate strength. Where the wrist or ankle has a thickness that causes the spring 5b to apply an excessive clamping force or a clamping force which is too weak, various disadvantages result, one of which is pain or discomfort experienced by the individual. If the individual has a wrist or ankle which is particularly stout, moreover, the limb cannot be passed through the clearance between the ends of the clamping plates 8, 8' even when the clamping plates are spread widely apart. This makes it impossible to attach the electrode to the limb.